Question

Suppose you are planning a trip in which a spacecraft is to travel
at a constant velocity for exactly eight months, as measured by a
clock on board the spacecraft, and then return home at the same
speed. Upon return, the people on earth will have aged exactly
seventy-five years. According to special relativity, how fast must
you travel? (Express your answer to at least 5 significant figures
as a multiple of c -- for example, 0.95585c.)